Legend has it she introduced herself saying: “My great-grandmother was the mistress of your great- great-grandfather – so how about it?” – a reference to King Edward VII and his mistress Alice Keppel.
The pair became lovers while Camilla was having a break from her on-off boyfriend, dashing army officer Andrew Parker Bowles.
But as Christopher Wilson, author of The Windsor Knot, Charles Camilla and the Legacy of Diana explains, marriage was a non-starter.
“Camilla ... was not aristocratic enough to be a royal bride,” he said.
“One of Charles’ friends even cruelly remarked: ‘Can you imagine her face on a postage stamp?’”
Camilla eventually went back to Andrew and they married in 1973 while Charles was away in the Royal Navy. They had two children, Tom and Laura, but Andrew was not averse to flings with other women and in 1986 Camilla resumed her affair with Charles.
Meanwhile, the prince had a string of failed romances and three turned down proposals of marriage behind him. By the end of the decade Charles was under increasing pressure from his parents to marry and produce the required ‘heir and spare’.
In July 1980, Charles began dating then 19-year- old Diana. They’d met up at party and the two connected. Even Camilla was in favour of his latest love interest. She met Diana for lunch, partly to make sure Diana wouldn’t get in the way as Camilla intended to continue to meet Charles at friends’ houses.
Charles proposed to Diana on February 6, 1981 and Diana recalled: “He said ‘will you marry me?’ and I laughed thinking ‘this is a joke’.
“And I said yeah, OK.
“He said, ‘I love you so much – whatever love means’ and ran upstairs to ring his mother,” Diana said.
But as their July 29, 1981 wedding day approached, Diana began to realise the depth of Charles’ relationship with Camilla.
“He’d found the virgin, the sacrificial lamb, and in a way he was obsessed with me, but it was hot and cold, hot and cold,” she later recalled.
When Diana told her sisters she couldn’t go through with the marriage, they laughed and said: “Well, bad luck Duch, your face is on the tea towels.”
The fairytale wedding in St Paul’s Cathedral was watched by 750 million people worldwide on TV but Christopher Wilson describes it as “the biggest con, the greatest fraud in royal history.”
He said: “As Diana walked up the aisle everyone of importance knew the marriage was a sham. It should have been called off because they were not matched, but tragically it went ahead.”
The couple quickly produced two children, William and Harry. But soon after Harry’s birth in 1984, the marriage began to collapse.
Diana’s police bodyguard Ken Wharfe witnessed the problems first-hand and recalls: “She knew the Prince of Wales had always had mistresses in the past, and she knew about Camilla, but she thought this time it would be different.
“But I don’t believe Charles’ affair with Camilla ever stopped.”
Charles began seeing Camilla regularly and Diana embarked on a series of affairs herself.
In 1989 at the 40th birthday party of Camilla’s sister Annabel Elliot, Diana confronted Camilla and Charles.
Wharfe said: “Diana told her, ‘I know what’s going on, so don’t treat me like an idiot.’
“Camilla replied: ‘It’s alright for you, you’ve got two lovely boys and everything you want.’
“I never understood that reply but it was the beginning of the end.”
In 1992 the lid blew off when Andrew Morton released his book Diana: Her True Story, which the Princess had secretly helped him with.
The infamous ‘Squidgygate’ and ‘Camillagate’ tapes followed, which revealed Diana was involved with other men and Charles was intimate with Camilla.
By December that year Prime Minister John Major informed the nation that the couple were separating.
In her 1995 Panorama interview, Diana sensationally admitted to an affair with army officer James Hewitt, but claimed she had been badly let down by Charles.
“There were three of us in the marriage so it got a bit crowded,” she famously said of Camilla.
In 1996 the couple divorced and Charles hoped to marry Camilla, who had been divorced from Andrew Parker Bowles.
Royal biographer Penny Junor claims the couple were going to “come out” in 1997 but their plans were paused by Diana’s death in Paris on August 31.
“Those and every other plan screeched to a halt when Britons woke up to the shocking news that Diana had been killed in a car crash.”
Charles married Camilla in 2005 and, now aged 72, she has become a popular member of the royal family.
Looking back, Morton recalled: “Charles did his best but he realised he couldn’t stop loving Camilla.
‘‘It was a different era and today Charles could have married Camilla in the first place because attitudes have changed.
“It’s ended up well for Charles and Camilla and they seem very happy, but it will always be a stain on the royal family that Diana was treated so badly.”
WATCH: Princess Diana was sent a 'surprise letter' by Camilla
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